`star` Cell Wall
`star` Endomembrane System
`star` Endoplasmic Reticulum


● A `color{violet}("non-living rigid structure")` called `color{violet}("the cell wall")` forms an outer covering for the `color{violet}("plasma membrane")` of `color{violet}("fungi and plants.")`

● `color{violet}("Cell wall")` not only gives shape to the cell and protects the cell from mechanical damage and infection, it also helps in `color{violet}("cell-to-cell")` interaction and provides barrier to undesirable macromolecules.

● Algae have cell wall, made of `color{brown}("cellulose, galactans, mannans")` and minerals like `color{brown}("calcium carbonate,")` while
in other plants it consists of `color{violet}("cellulose, hemicellulose, pectins")` and `color{violet}("proteins.")`

● The `color{violet}("cell wall")` of a young plant cell, the `color{brown}("primary wall")` is capable of growth, which `color{violet}("gradually diminishes")` as the cell matures and the secondary wall is formed on the inner (towards membrane) side of the cell.

● The middle `color{violet}("lamella")` is a layer mainly of `color{brown}("calcium pectate")` which holds or glues the different neighbouring `color{violet}("cells together.")`

● The `color{violet}("cell wall")` and `color{violet}("middle lamellae")` may be traversed by `color{brown}("plasmodesmata")` which connect the cytoplasm of `color{violet}("neighbouring cells.")`


● While each of the `color{brown}("membranous organelles")` is distinct in terms of its structure and function, many of these are considered together as an `color{violet}("endomembrane system")` because their functions are coordinated.

● The `color{violet}("endomembrane system")` include `color{brown}("endoplasmic reticulum (ER), golgi complex, lysosomes")` and `color{brown}("vacuoles.")`

● Since the functions of the `color{brown}("mitochondria, chloroplast and peroxisomes")` are not coordinated with the above
components, these are not considered as part of the `color{violet}("endomembrane system")`.


● `color{violet}("Electron microscopic")` studies of `color{violet}("eukaryotic cells")` reveal the presence of a `color{violet}("network or reticulum")` of tiny tubular structures scattered in the cytoplasm that is called the `color{brown}("endoplasmic reticulum (ER).")`

● Hence, ER divides the intracellular space into two distinct compartments, i.e., luminal (inside ER) and extra luminal (cytoplasm) compartments.

● The ER often shows `color{brown}("ribosomes")` attached to their outer surface.

● The `color{violet}("endoplasmic reticulum")` bearing ribosomes on their surface is called `color{brown}("rough endoplasmic reticulum (RER).")`

● In the absence of ribosomes they appear smooth and are called `color{brown}("smooth endoplasmic reticulum (SER).")`

● `color{violet}("RER")` is frequently observed in the `color{violet}("cells")` actively involved in `color{violet}("protein synthesis and secretion.")`

● They are `color{violet}("extensive and continuous")` with the outer membrane of the `color{violet}("nucleus.")`

● The smooth `color{violet}("endoplasmic reticulum")` is the major site for `color{violet}("synthesis of lipid.")`

● In `color{violet}("animal cells lipid-like steroidal hormones")` are `color{violet}("synthesised in SER.")`